1. Field of the Invention
The present invention generally relates to distance measurement, and more specifically to a system and method for distance measurement by inphase and quadrature signals in a radio system.
2. Related Art
Distance measurement systems are required in a wide variety of applications. Surveying, position determination, precision farming and mining are some example applications that require distance measurement systems.
In recent years, various systems for distance measurement systems have been developed. The global positioning satellite (GPS) system operated by the United States Department of Defense, for example, is a highly complex system of determining the position of an object by distance measurement. The GPS system depends on measuring the time-of-flight of signals from three or more orbiting satellite transmitters by a navigation receiver. According to the GPS system, each satellite broadcasts a time-stamped signal that includes the satellite's ephemeris, i.e., its own position. When the mobile unit receives a GPS signal, the mobile unit measures the transmission delay relative to its own clock and determines the distance from the transmitting satellite's position.
Another approach is that employed by the U.S. Navy's TRANSIT system. In that system, a mobile unit performs continuous doppler measurements of a signal broadcast by a low earth orbit (LEO) satellite. The measurements continue for several minutes. The system usually requires two passes of the satellite, necessitating a wait of more than 100 minutes. In addition, because the distance and position calculations are performed by the mobile unit, the satellite must broadcast information regarding its position, i.e., its ephemeris. Although the TRANSIT system is capable of high accuracy (on the order of one meter), the delay required is unacceptable for commercial applications.
Although these systems accurately measure the distance between objects, they are extremely complex, and, more importantly, expensive to implement. For example, both the GPS and TRANSIT systems require multiple satellites, sophisticated receivers and antennas that require hundreds of millions dollars of investments. Also, response times of GPS and TRANSIT systems are typically slow due to their narrow bandwidth. Furthermore, since these systems depend on orbiting satellites, they require an unimpeded view of the sky to effectively perform range measurement. For these reasons, it has been recognized that there is a need for a simple, low cost distance measurement system.